1. Field of the Invention
The present invention relates generally to an image forming apparatus, and more particularly to an image receiving sheet transport system used for an image forming apparatus which forms an image by superimposing and pressing a photosensitive sheet coated with light and pressure sensitive microcapsules containing photosetting materials and coloring dyes onto an image receiving sheet coated with developer which reacts with the coloring dyes to develop colors. The image receiving sheet transport system transports an image receiving sheet after the image receiving sheet has been pressed together with a photosensitive sheet superimposed thereon.
2. Description of the Prior Art
When a photosensitive sheet coated with light and pressure sensitive microcapsules containing photosetting materials and coloring dyes is exposed to image forming light such as light reflected from a document, the microcapsules struck by the light harden to form a latent image. On the thus formed latent image, an image receiving sheet coated with developer which reacts with the coloring dyes contained in the microcapsules to develop colors is superimposed and pressed together, which causes unhardened microcapsules to rupture and the coloring dyes contained therein to flow out onto the image receiving sheet, thus developing the latent image.
The image receiving sheet and the photosensitive sheet superimposed thereon are pressed together using a pressure developing device. The pressure developing device is so constructed as to apply and release pressure, the pressure being applied only during the pressure developing process in which the image receiving sheet with the photosensitive sheet superimposed thereon is passed therethrough. That is, when the leading edge of the latent image formed on the photosensitive sheet and the leading edge of the image receiving sheet reach the pressure developing device, the pressure developing device theretofore in a pressure release condition works to apply pressure onto the leading edges, and when the trailing edges of the image receiving sheet and the latent image on the photosensitive sheet reach the pressure position in the pressure developing device, the pressure is released.
The image receiving sheet passed through the pressure developing device is transported on to a gloss imparting unit, hereinafter referred to as "glosser unit", where it is treated with heat and pressure. Application of heat and pressure accelerates the coloring reaction of the coloring dyes, while causing thermoplastic resin, with which the image receiving sheet is pre-coated, to soften and melt to cover the surface of the image receiving sheet, thereby giving a glossy finish to the image.
When the pressure is released with the trailing edge of the image receiving sheet reaching the pressure position in the pressure developing device, the pressure developing device stops transporting the image receiving sheet, but the glosser unit continues to run. As a result, though for a moment, the trailing edge of the image receiving sheet remains pressed by the pressure developing device while it is not being transported, and the leading edge of the image receiving sheet, which has already reached the glosser unit, is kept from further transportation because of the pulling force applied from the trailing edge thereof. As a result, the leading edge of the image receiving sheet is subjected to excess heat by the glosser unit, thereby giving rise to the possibility of offset in which the developer on the image receiving sheet adheres to the glosser unit.